With the development of the semiconductor industry, integrated circuits with higher performance and more powerful functions require greater element density. Thus, the sizes of the components need to be scaled further. Accordingly, in order to improve the performance of the Metal Oxide Semiconductor Field Effect Transistor (MOSFET), the gate length of the MOSFET should be further reduced. However, with the continuous reduction of the gate length, when the gate length is reduced to approach the width of the depletion layer of the source and the drain, for example less than 40 nm, severe short channel effects occur, which disadvantageously leads to deterioration of device performance and difficulty for large scale production of integrated circuit. One of the short channel effects is that the threshold voltage of MOSFET decreases with the reduction of the gate length, thereby rendering a rapid increase of leakage current when the gate length is short. It has become a challenge in large scale production of integrated circuits to alleviate the short channel effects and effectively control the low threshold voltage caused by the decrease of the gate length.
A method for controlling and alleviating the short channel effects by introducing reverse Halo implantation region in a channel is depicted in the paper by Zhu H et al., On the Control of Short-Channel Effect for MOSFETs With Reverse Halo Implantation, IEEE ELECTRON DEVICE LETTERS, vol. 28, No. 2, pages 168-170, 2007. By implanting n-type dopants using high energy in the channel of NMOS devices, the amount of the n-type dopants in the channel region of NMOS devices with shorter gate length is less than that of the n-type dopants in the channel region of NMOS devices with longer gate length because gate stack with longer gate length will block more implanted dopants, thus the threshold voltage of NMOS devices with shorter gate length may be higher, and the short channel effects may be alleviated. Such a method may also be performed on the PMOS devices by implanting p-type dopants using high energy.
However, all the existing reverse Halo implantation methods are performed after formation of the gate stack. Furthermore, the reverse Halo dopants should penetrate through the gate stack to reach the channel region, which may disadvantageously lead to deterioration of the gate stack and cause gate leakage current. Moreover, by using metal gate, it is difficult for the reverse Halo dopants to penetrate through the metal gate, which will cause failure of reverse Halo implantation.
Therefore, for the purpose of improving the manufacture of high-performance semiconductor device, there is a need to provide a semiconductor device capable of forming a reverse Halo implantation region in a channel and a method of manufacturing the same, to thereby alleviate the short channel effects without deteriorating the performance of the metal grate stack.